As mobile device technology continues to develop and demand therefor continues to increase, demand for secondary batteries as energy sources is rapidly increasing. Among secondary batteries, lithium secondary batteries, which have high energy density and operating voltage, long cycle lifespan, and low self-discharge rate, are commercially available and widely used.
In addition, as interest in environmental problems is recently increasing, research into electric vehicles (EVs), hybrid EVs (HEVs), and the like that can replace vehicles using fossil fuels, such as gasoline vehicles, diesel vehicles, and the like, which are one of the main causes of air pollution, is actively underway. As a power source of EVs, HEVs, and the like, a nickel metal-hydride secondary battery is mainly used. However, research into lithium secondary batteries having high energy density, high discharge voltage and output stability is actively underway and some lithium secondary batteries are commercially available.
Conventional lithium ion secondary batteries generally use a lithium cobalt composite oxide as a cathode and a graphite-based material as an anode. However, study is recently being conducted with regard to using a spinel-structure lithium nickel-based metal oxide as a cathode and a lithium titanium oxide as an anode active material instead of the conventional materials.
In such lithium secondary batteries, charging and discharging processes are performed while lithium ions of a cathode are repeatedly intercalated into and deintercalated from an anode. Although there are differences in theoretical capacities of batteries according to kinds of electrode active materials, in most cases, charge and discharge capacities are deteriorated as cycles proceed.
Such phenomenon is mainly attributed to non-functioning of active materials due to separation of electrode active material components or separation between an electrode active material and a current collector by change in volume of an electrode occurring as charging and discharging of a battery proceed. In addition, in the intercalation and deintercalation processes, lithium ions intercalated into an anode are unable to be properly deintercalated therefrom and thus an anode active site is reduced and, accordingly, charge and discharge capacities and lifespan characteristics of a battery are deteriorated as cycles proceed.
Therefore, there is an urgent need to develop technology which may impart high adhesion between an active material and a current collector to improve battery capacity, and, at the same time, may exhibit superior electrical conductivity to improve battery performance.